Patent GB-858885-A (GB)
Title: Fuel supply system for gas turbine engines
IPC: F02C9/16
Filed: 1959-04-01
Abstract: 858,885. Gas turbine engine fuel systems. BENDIX CORPORATION, [formerly BENDIX AVIATION CORPORATION]. April 1, 1959 [May 28, 1958], No. 11088/59. Class 110 (3). [Also in Group XXIX] In a fuel supply system for a gas turbine engine of the kind having a separate power turbine, means responsive to a pressure generated by the engine compressor are provided for controlling the supply of fuel to the engine as a function of compressor pressure. A first device responsive to the speed of one of the turbines is provided for modulating this pressure to vary the fuel flow as a function of that speed, and a second device responsive to the speed of the second turbine is provided for modulating this pressure to control the fuel supply as a function of the second turbine speed. The plant shown in Fig. 1 comprises a compressor 12, combustion equipment 18, compressor driving turbine 14 and a separate power turbine 26. Fuel is supplied from tank 78 through pump 76 and fuel control unit 46 through duct 48 to the ring manifold 22. The control unit is connected through duct 35 to compressor outlet pressure, and by means of gearing and shaft 42 to the shaft 16 connecting compressor 12 and turbine 14. Throttle lever 52 is mounted on shaft 50 and is connected by lever 62 to a lever 58 mounted on shaft 56. An air duct 64 connects the fuel control unit 46 to a speed control unit 70 which is connected by gearing and shaft 66 to the output shaft 28 of the separate power turbine 26. Fuel from the pump 76 at pressure P 0  enters the control unit at 98 and passes through gear pump 100 where its pressure is increased to P 1 , and discharges to annulus 102 discharging therefrom through duct 104 and filter screen 108 to duct 110. A high-pressure relief valve 106 is disposed between annulus 102 and pump inlet 98. Fuel from duct 110 passes by way of metering valve 112 and duct 114, controlled by valve 116, at pressure P 2  to duct 48 and thence to combustion equipment 18. A by-pass valve 124 controls flow of fuel at pressure P 1  in duct 122 back to the intake of gear pump 100 through duct 126, the valve being controlled by a diaphragm 128 which tends to move to the right by pressure of fuel P 1  and to the left by pressure of fuel P 2  in duct 120; the spring 130 also exerts a force on the diaphragm acting to the left. The position of the valve 116 is determined by the setting of the throttle lever 52 acting on eccentric shaft 50. The position of the fuel metering valve 112 is determined by the position of the bell-crank lever 140, one of the arms of which is controlled by means of two bellows 142, 144 disposed in the chamber 146 which is connected to fuel pressure P 0 . The bellows 142 is either evacuated and sealed or vented to atmospheric pressure. The bellows 144 is connected to compressor outlet pressure through duct 35, orifice 147 and duct 145, the duct 145 also being connected through ducts 148 and 150 to an outlet 151 into a chamber 170 which is vented to atmosphere through outlet 168. The duct 148 also connects through duct 64 to the speed control unit 70. The outlet 151 is controlled by a half-ball valve 152 carried by a lever 154 pivoted at 166. The lever 154 is acted on by a spring 156 which acts to close the outlet 151, the tension of the spring being controlled by lever 58 acting on eccentric shaft 56, the position of the lever 58 being determined by the position of the throttle lever 52. The lever 154 is acted on in the opposite direction by means of centrifugal weights 160 driven at engine speed by means of shaft 162, the weights 160 tending to open the outlet 151 with increase in speed. The speed control unit 70 is shown in Fig. 4 and comprises a pivoted lever arm 194 acted on by a spring 196 and centrifugal weights 200 similar to the fuel control unit, the centrifugal governor unit being driven at the speed of the free power turbine 26 by means of shaft 66. The lever arm 194 controls the outlet 190 of the duct 188 which is connected to the duct 64 leading from the fuel control unit. The chamber 208 is vented to atmosphere through outlet 206. The tension of the spring 196 may be adjusted by means of the eccentric shaft 72 and then set. Should it be desired to reduce the power being delivered to the propeller 32, the throttle 52 and lever 58 are moved to the reduced power position, the movement of the lever 58 producing a reduction in tension of the spring 156 so that the outlet 151 tends to open thereby producing a reduction of pressure in the bellows 144. The bell-crank lever 140 tends to move in an anti-clockwise direction so causing the metering valve 112 to move in a flow-decreasing direction. The speed of the turbine is consequently reduced so that the weights 160 allow the lever arm 154 to move downwardly and the balance of the arm is restored. Movement of the throttle to increase power causes the valve 152 to close the outlet. 151, increased pressure in the bellows 144 causes the lever 140 to move clockwise and so increases the area of the fuel metering orifice. The speed control unit 70 is provided to prevent overspeeding of the power turbine 26 when the throttle is moved rapidly to maximum power position. Should the speed of the power turbine 26 exceed the maximum allowable, the governor weights 200 cause the outlet 190 to open which produces reduction in pressure in the bellows 144 and so movement of the metering valve 112 to cause decrease in supply of fuel to the engine. In a second embodiment, the lever 58 is transposed from the fuel control unit 46 to the speed control unit 70, so that movement of the throttle lever 52 produces variation in the tension of the spring 196 in the speed control unit, the tension of the spring 156 in the fuel control unit being fixed. To increase the speed of the power turbine, the throttle is moved in a speed-increasing direction which rotates the shaft 72 so as to increase the tension of the spring 196 and so the closing force on the valve 192. Increase in pressure of the air in bellows 144 causes the metering valve 112 to move in a flow-increasing direction. In this case the portion of the fuel control unit 46 containing lever 154, spring 156 and governor weights 160 is utilized as a speed-limiting device.